This invention relates to aquarium filters, and more specifically to an external aquarium filter utilizing a pump impeller which is magnetically driven by a removable power unit.
Aquarium filters are utilized for aeration, circulation and filtration of the aquarium water. One type of aquarium filter is the externally mounted filter which houses filtration equipment and includes a pumping mechanism which induces the circulation of water from the aquarium tank through the filtration equipment and then returns the clean water to the aquarium. The pumping mechanism is generally provided within the water flow path. Some filters utilize a hermetically enclosed pump which is placed directly within the flow path. Others place an impeller in the flow path and magnetically couple the impeller to a driving unit.
An aquarium filter assembly of a type using a magnetically coupled impeller is described in U.S. Pat. No. 4,512,885 assigned to the assignee of the present invention. Such aquarium filter assembly includes a filter box which is adapted to be mounted on a wall of an aquarium tank and contains an inlet chamber for receiving contaminated water from the aquarium tank, and a filter chamber for filtering the contaminated water and directing the filtered water to flow back into the aquarium tank. A removable unitary assembly is supported on the filter box and includes an intake tube for insertion into the aquarium tank and a discharge tube positioned in the inlet chamber. A pump impeller unit depends from the end of the discharge tube. The impeller unit includes a rotor shaft on which is mounted a magnet. A stator unit is removably coupled to the filter box so that it is magnetically coupled to the magnet on the rotor shaft, whereby it drives the rotor through a magnetic flux relationship.
Although the impeller unit is within the flow path of the water, the electromagnetic stator elements are fluidically sealed from the flow path. In the aforementioned U.S. Patent a tube depends from the filter box and the rotor shaft sits in the tube. The stator unit includes an aperture between the legs of the stator laminations for receiving the depending tube. In a variation of this filter assembly, the stator unit includes a fluidially sealed well formed between the legs of the stator laminations for directly receiving the impeller unit.
The stator unit is generally provided as a housing forming a separate power unit. The power unit is removably mounted onto the filter box. Typically, an aperture is provided in the inlet chamber of the filter box from which the magnet impeller assembly depends. The power unit includes a hollow cylindrical stem portion which locks into the aperture and defines the mouth of the well in the power unit into which the magnetic impeller assembly sits. An O-ring is situated around the cylindrical stem and fluidially seals the connection between the power unit and the aperture.
The power unit houses stator laminations with an electromagnetic coil winding. The coil is connected to a source of electricity and provides the necessary magnetic flux flow path through the laminations for driving the magnetically coupled rotor. A potting compound surrounds the laminations and the coil for protecting these electromagnetic elements and preventing water from reaching them.
During normal operation, the water drawn in by the impeller will fill the inlet chamber of the filter box and the well in which the magnetic impeller assembly sits. The flow of water around the magnetic impeller assembly provides adequate cooling of the heat generated by the power unit. During such normal operation, the flow of water is sufficient to keep the temperature reduced to avoid damage to the filter box.
When the filter stops through power failure and doesn't restart, or when the impeller gets blocked, the flow of water through the filter stops. The existing water in the filter tends to evaporate. Such evaporation more easily takes place adjacent the power unit because of the heat generated by this unit. With the water evaporated from the well, there is insufficient cooling of the power unit. The heat is coupled through the O-ring to the aperture of the filter box and has a tendency of causing slight deformation or melting around the aperture of the filter box. Such deformation or melting causes leaks at the aperture.
Even though the blockage is removed or the filter is restarted, the leaks continue around the aperture and the entire filter box must be replaced.
Accordingly, while such aquarium filter assemblies have been found to be exceedingly useful, on the occasion of the filter running dry, heating of the filter has caused leaks to the filter box.